1. Field of the Invention
The present invention relates to a cooling system of a semiconductor testing device, particularly to a cooling system of a semiconductor testing device for controlling the number of revolutions of a fan so as to obtain airflow corresponding to a heating value of a measuring unit by use of the fan which is driven by a DC motor, thereby preventing a power from being wasted.
2. Prior Art
A semiconductor testing device generally comprises a body 200 and test heads 300 as shown in FIG. 3(A), wherein electric characteristics of a device to be measured mounted on the test heads 300 is tested by the body 200, namely, by the control carried out by the body 200.
In such a semiconductor testing device, there has been employed a system shown in FIG. 4 for cooling a measuring unit 80A which is a mounted in the body 200 or in the test heads 300.
That is, in FIG. 4, a fan 60A is provided adjacent to the measuring unit 80A, wherein a three-phase AC motor 62A of the fan 60A is rotated to suck air heated by heat produced by the measuring unit 80A.
At this time, since there produces a negative pressure at the part where air is sucked, outside cool air is taken in this part through an open portion of the measuring unit 80A provided at the opposing position of the fan 60A.
As a result, the measuring unit 80A dissipates or radiates heat so that the measuring unit 80A is cooled.
In this case, the number of revolutions of the three-phase AC motor 62A for driving the fan 60A is determined by a frequency of the AC power supply of the motor and the number of poles of a revolving field of the motor. From this, the number of revolutions of the three-phase AC motor 62A has generally a specific fixed value.
That is, the following well known relationship or expression is established in the three-phase AC motor 62A suppose that the number of revolutions is Nac (unit: rps), the frequency of AC power supply is F (unit: Hz), and the number of poles of the revolving field is p. EQU Nac=2F/p (1)
In the expression (1), the frequency F of the AC power supply is generally 50 Hz or 60 Hz, and the number of poles p of the revolving field is a fixed value which is determined when manufacturing a motor.
Accordingly, the number of revolutions Nac of the three-phase AC motor 62A becomes a fixed value as evident from the expression (1).
The air-flow to be needed for cooling the measuring unit 80A is determined by the number of revolutions Nac of the three-phase AC motor 62A and a sectional area of the fan 60A.
Further, in FIG. 4, a temperature sensor 50A is generally a thermal relay type which operates when the temperature exceeds a specific temperature (anomalous temperature region), and the operating modes of the relay (ON/OFF) are transmitted to a power supply controller 70 via a signal cable 51A.
Accordingly, the power supply controller 70 cuts off a power supplied to the measuring unit 80A via a power supply cable 81A. That is, the measuring unit 80A has been conventionally cooled by the fan 60A employing the three-phase AC motor 62A, and the power supply has been cut off when an ambient temperature of the measuring unit 80A reaches an anomalous temperature region.
In the prior art as mentioned above in FIG. 4, the air-flow needed for cooling the measuring unit 80A is determined by the number of revolutions Nac of the three-phase AC motor 62A and the sectional area of the fan 60A.
However, as evident from the expression (1), since the number of revolutions Nac of the three-phase AC motor 62A is a fixed value and the sectional area of the fan 60A is constant, the air-flow presented for cooling the measuring unit 80A is invariant regardless of whether the measuring unit 80A is in standby condition (heating value Qa is small) or in operating condition (heating value Qa is large) when the three-phase AC motor 62A is used.
For example, suppose that the semiconductor detecting device shown in FIG. 3(A) has measuring units U1, U2, U3 and there are operating modes shown in FIG. 3 (B) wherein standby condition is denoted by x and operating condition denoted by .largecircle..
Of these operating modes, all measuring units U1 to U3 are in operating condition in the case of a, and the measuring units U2 and U3 are in operating condition while other measuring unit U1 is standby condition in the case of b, and one measuring unit U1 is in operating condition while the other measuring units U2 and U3 are in standby condition in the case of c, and all the measuring units U1 to U3 are in standby condition in the case of d.
Accordingly, in the case of FIG. 3(B), the heating value Qa is the largest in the case of a and it decreases in the order of b and c, and it is the smallest in the case of d. That is, there occurs a case where the power to be consumed by, i.e., the heating value of the measuring units is varied according to the operating condition or standby condition depending on devices to be used in the semiconductor testing device (FIG. 3(A)).
However, air-flow needed for cooling the measuring unit can not be changed corresponding to the heating value Qa because the fan 60A which is driven by the three-phase AC motor 62A has been used.
Accordingly, even if the measuring unit 80A is in standby condition, there is needed air-flow which is the same as that for cooling the measuring unit 80A in a state of the maximum heating value. For example, even in the state of d in FIG. 3(B) (all the measuring units are in standby condition), there requires air-flow needed for cooling in the case of a (all the measuring units are in operating condition).
Accordingly, even in standby condition, i.e., in the case of d, the number of revolutions of the fan 60A increases by the air-flow needed for cooling the measuring unit 80A in the case of a, thereby power is consumed more than it is needed, and hence power is wasted.